For purposes of data communication, it is known to use multi-carrier signal communication. One form or type of multi-carrier signal communication is the Digital Subscriber Line (DSL) technology. In order to improve performance of the DSL technology, it is known to use a technique which is referred to as “vectoring” or “vectored data transmission”.
In vectoring or vectored data transmission, transmission or reception of data between a plurality of transmitters and a plurality of receivers via a plurality of communication connections is coordinated in order to improve the transmission, for example to reduce the influence of crosstalk. Either transmitters or receivers are co-located.
In DSL transmission systems, for example VDSL (very high bit rate DSL) transmission systems, data may be transmitted from a central office (CO) or other provider equipment to a plurality of receivers located in different locations, for example in customer premises (CPE), via a plurality of communication lines. Crosstalk resulting from signals on different lines transmitted in the same direction, also referred to as far end crosstalk (FEXT), may result in reduced data throughput. Through vectoring, signals transmitted over the plurality of communication lines from the central office or received via the plurality of communication lines in the central office may be processed jointly in order to reduce such crosstalk, which joint processing corresponds to the above-mentioned vectoring. In this respect, the reduction of crosstalk by coordinated transmission of signals is sometimes referred to as crosstalk precompensation, whereas the reduction of crosstalk through joint processing of received signals is sometimes referred to as crosstalk cancellation. The communication connections which are processed jointly are sometimes referred to as a vectored group.
Both at the initialization of communication and during communication, it may be necessary to add an additional communication connection to the vectored group, for example when an additional user of a DSL service becomes active. In such cases, a training has to be performed to determine the influence from the communication connection to be added to the vectored group to the communication connections already in the vectored group and vice versa to cancel the crosstalk. Training may also become necessary if crosstalk characteristics between different communication connections change for some reason.
During training of a vectored DSL system, it is known to send a multi-carrier training signal from a central office (CO) to a customer premises equipment (CPE). At the CPE, an individual error value is evaluated for each signal carrier. The individual error values are then transmitted back to the CO on a backchannel of the communication connection and used for adapting crosstalk cancellation parameters.
Since transmitting the individual error values on the backchannel requires bandwidth, there is a need for efficient error reporting techniques in multi-carrier signal communication.